/*
 * CXSparse: a Concise Sparse matrix package.
 * Copyright (C) 2006-2011, Timothy A. Davis.
 * Copyright (C) 2011-2012, Richard W. Lincoln.
 * http://www.cise.ufl.edu/research/sparse/CXSparse
 *
 * -------------------------------------------------------------------------
 *
 * CXSparseJ is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * CXSparseJ is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this Module; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
 *
 */

package scu.maqiang.cxsparsej;

import java.util.Random;

/**
 * Random permutation.
 *
 * @author Piotr Wendykier (piotr.wendykier@gmail.com)
 * @author Richard Lincoln (r.w.lincoln@gmail.com)
 *
 */
public class DZcs_randperm {

	/**
	 * Returns a random permutation vector, the identity perm, or p = n-1:-1:0.
	 * seed = -1 means p = n-1:-1:0. seed = 0 means p = identity. otherwise p =
	 * random permutation.
	 *
	 * @param n
	 *            length of p
	 * @param seed
	 *            0: natural, -1: reverse, random p otherwise
	 * @return p, null on error or for natural order
	 */
	public static int[] cs_randperm(int n, int seed)
	{
		int p[], k, j, t ;
		Random r ;
		if (seed == 0) return (null) ;		/* return p = NULL (identity) */
		p = new int [n] ;			/* allocate result */
		if (p == null) return (null) ;		/* out of memory */
		for (k = 0 ; k < n ; k++) p [k] = n-k-1 ;
		if (seed == -1) return (p) ;		/* return reverse permutation */
		r = new Random(seed) ;			/* get new random number seed */
		for (k = 0 ; k < n ; k++)
		{
			j = k + r.nextInt(n - k) ;	/* j = rand int in range k to n-1 */
			t = p [j] ;			/* swap p[k] and p[j] */
			p [j] = p [k] ;
			p [k] = t ;
		}
		return (p);
	}

}
